Along with the rapid distribution of information-related equipment and communication equipment such as personal computers, video cameras and mobile telephones in recent years, more emphasis is placed on the development of batteries that are used as power sources of the equipment. Furthermore, development of high output power and high capacity batteries for electric vehicles or hybrid vehicles is in progress in automobile industries and the like as well. Currently, lithium batteries are attracting more attention among a variety of batteries, from the viewpoint of having high energy density.
In lithium batteries that are currently available in the market, since liquid electrolytes containing flammable organic solvents are used, installation of a safety device for suppressing temperature increase at the time of a short circuit, or an apparatus intended for preventing short circuits is needed. In this regard, it is speculated that since a lithium battery obtained by converting a battery to an all solid state battery by replacing the liquid electrolyte with a solid electrolyte layer, does not use a flammable organic solvent in the battery, simplification of safety devices is promoted, and the lithium battery is excellent in terms of production cost and productivity.
Regarding the solid electrolyte material used in all solid lithium batteries, sulfide solid electrolyte materials are known. For example, Patent Literature 1 discloses a LiSiPS-based sulfide solid electrolyte material (argyrodite type). Also, for example, Patent Literature 2 discloses a sulfide solid electrolyte material having a composition of Li(4-x)Ge(1-x)PxS4.